Replacing dietary fish oil with increasing levels of rapeseed oil and olive oil -: effects on Atlantic salmon (Salmo salar L.) tissue and lipoprotein lipid composition and lipogenic enzyme activities

Six groups of Atlantic salmon, initial weight 142 +/- 1 g, were fed increasing dietary inclusion of rapeseed oil (RO) in a regression design and one group was fed a 50% olive oil/50% capelin oil diet. Fatty acid composition was measured in red and white muscle, liver, and fatty acid and lipid class composition was measured in plasma and in the lipoproteins; very low density lipoprotein, low density lipoprotein, high density lipoprotein and nonlipoprotein fraction after 22 and 42 weeks of feeding. Further, the activities of liver NADH-isocitrate dehydrogenase (ICDH), malic enzyme, glucose-6-phosphate dehydrogenase (G6PDH) and 6-phosphogluconate dehydrogenase were measured at each sampling point. After 42 weeks of feeding the experimental diets, the tissue and lipoprotein fatty acid composition was highly affected by dietary fatty acid composition. Regressions showed that 22:1n - 11, 18:1n - 9, 18:3n - 3 and 18:2n - 6 are readily metabolized in all tissues analysed. Further, 20:5n - 3 seems to be metabolized in muscle and retained in liver. 22:6n - 3 was selectively retained in all the analysed tissues, and with higher retention in liver and plasma with higher polar lipid/neutral lipid ratio compared to white and red muscle. Liver from salmon fed 100% RO showed decreased G6PDH and increased ICDH activities compared to the other dietary groups; however, no linear relationship related to increased RO inclusion was detected. The amount of plasma lipoproteins, liver monoene fatty acid level and lipogenic enzyme activity decreased from the autumn to the winter sampling with concomitant decrease in temperature.